But even as normal operations out of the three ports are quickly resuming, the world's major cruise lines are facing months of disruptions to itineraries that include stops at Eastern Caribbean islands that Irma hit hard.

Already, Norwegian Cruise Line has announced it is replacing all Eastern Caribbean sailings with Western Caribbean sailings through at least November.

Norwegian's Eastern Caribbean voyages — currently offered out of Miami on a single ship, the 4,248-passenger Norwegian Escape — traditionally feature a stop in St. Thomas, which has suffered what local officials have called catastrophic damage. The trips also include a visit to nearby Tortola in the British Virgin Islands, which also was devastated by Irma, according to local officials.

Royal Caribbean also has said its ships won't be able to visit St. Thomas as well as Irma-ravaged St. Martin and Key West, Fla., for some time, although it hasn't given an outlook on how long they might stay away.

Royal Caribbean ships regularly dock on the Dutch side of the island of St. Martin, known as St. Maarten.

"Given Hurricane Irma's impact to St. Maarten, St. Thomas and Key West, we will be working on (finding) alternative ports for future sailings until these islands have fully recovered," Royal Caribbean said Monday in a travel alert for customers posted on its website.

St. Thomas and St. Martin are two of the Caribbean destinations most visited by cruise ships and integral to dozens of cruise itineraries. Each draws more than 1.6 million cruisers per year. In the Caribbean and the Bahamas, only a handful of ports come close to drawing as many passengers.

In addition to St. Thomas, St. Martin, Tortola and Key West, Fla., cruise ship destinations significantly affected by Irma include St. John, Barbuda, St. Barts and Cuba. The latter only had recently opened up to U.S.-based cruise ships.

It was a widely spread blow that stunned even longtime industry watchers.

"This is unprecedented to have so many Caribbean islands devastated all at once," Mike Driscoll, editor of Cruise Week, told USA TODAY. "In the past it has been one or two islands at once knocked out temporarily by a big storm. This is different in scale."

Driscoll said that while it's early days in the recovery effort on hard-hit Caribbean islands, it's already looking like a massive amount of work will be needed to help several of them recover to the point where cruise ships can return — work that could take an extended period.

Cruise lines haven't talked much in the past few days about how long they might have to divert ships from the affected islands. For now, they're focused on relief efforts. But in a research note sent to investors on Monday, Instinet analyst Harry Curtis estimated it could take "several quarters or more" to repair infrastructure on St. Martin and St. Thomas, suggesting it could be months before ships return.

Still, the situation for cruise lines in the Caribbean isn't as dire as it may seem. Curtis noted several other islands in the Eastern Caribbean that are visited by cruise ships — including Antigua, St. Kitts and Puerto Rico — were spared major damage. The storm also caused no damage to cruise ports in the Western Caribbean such as Cozumel and Costa Maya, Mexico; Harvest Caye, Belize; and Falmouth, Montego Bay and Ocho Rios in Jamaica. That leaves plenty of places in the Caribbean for cruise ships to go.

"The upshot is that some Eastern Caribbean sailings will divert to (Eastern Caribbean) islands less affected and to western ports," Curtis said.

As of Wednesday, there also had been no reports of damage to the cruise line private islands that are a significant part of many itineraries, most of which are located in The Bahamas.

One factor softening the impact of Irma on the cruise industry is that the storm barreled through the Caribbean during the low season for cruising in the region, when there are fewer ships on hand. September and October is a time when many vessels that spend winters in the Caribbean still are coming back from summer postings in Europe and Alaska.

"In a certain sense cruise lines are fortunate," Driscoll said. "The number of canceled sailings was not as bad as it could have been."

Still, there are longer-term effects on the cruise industry to consider.

"The basic message potential Caribbean vacationers heard this past week was that the Caribbean was devastated," Driscoll noted. "That could cause a lot of people to put off taking a Caribbean cruise."